1. Field of the Invention
The present invention relates to an oven controlled crystal oscillator (OCXO: Oven Controlled Crystal Oscillator), more particularly to an oven controlled crystal oscillator which, when a circuit component is soldered on a substrate, reduces an occurrence of cracks in the solder and improves reliability.
2. Description of the Related Art
[Prior Art]
In order to increase frequency stability, an oven controlled crystal oscillator attempts to stabilize frequency by controlling, in a thermostatic oven, the temperature of components having a large temperature effect in a wide temperature range.
The temperature control in the oven controlled crystal oscillator is generally carried out such that a control circuit that controls a thermostatic oven carries out temperature control with a differential direct-current amplifier by a resistance bridge using a thermistor. When on/off of a power source of the thermostatic oven is repeated, a heat cycle is burdened on a using part/material, which causes a problem in reliability.
[Circuit Component Mount Example: FIG. 13, FIG. 14]
Explained is a conventional case where a large circuit component (a large-sized circuit component) is mounted on a substrate of a crystal oscillator, with reference to FIG. 13 and FIG. 14. FIG. 10 is a planar explanatory view of a state where a large-sized circuit component is mounted, and FIG. 14 is a cross-sectional explanatory view of the state where a large-sized circuit component is mounted.
As shown in FIG. 13 and FIG. 14, a large circuit component (a large-sized circuit component) 2 is fixed by a solder 10 on a substrate 1 made of a glass epoxy resin.
Note that, FIG. 13 and FIG. 14 are simplified views in which a single large-sized circuit component 2 is mounted on a small substrate 1, for convenience of explanation. However, on a real substrate 1, a crystal oscillator, a plurality of large and small circuit components, and the like are mounted.
[Related Art]
Note that, as related prior art technology, there are the followings: Japanese Patent Application Laid-Open No. 2007-214307, “Electronic Device,” (EPSON TOYOCOM CORPORATION) [Patent Document 1]; Japanese Patent Application Laid-Open No. 08-237031, “Piezoelectric Oscillator,” (Kinseki Co., Ltd.) [Patent Document 2]; Japanese Utility Model Application Laid-Open No. 62-037428, “Piezoelectric Oscillator,” (Kinseki Co., Ltd) [Patent Document 3]; Japanese Patent Application Laid-Open No. 2006-014208, “Crystal Oscillator,” (NIHON DEMPA KOGYO CO., LTD.) [Patent Document 4]; and Japanese Patent Application Laid-Open No. 2009-284372, “Constant Temperature Structure of Crystal Oscillator,” (NIHON DEMPA KOGYO CO., LTD.) [Patent Document 5].
Patent Document 1 discloses that in an electronic device, an opening 38 and a slit portion 40 are provided on a substrate 30 on an underside of an electronic component to reduce an occurrence of cracks in a sealant 12 due to air expansion.
Patent Document 2 discloses that in a piezoelectric oscillator, a slit 5 is formed to surround an oscillation circuit component 3 disposed on a substrate 4, thereby making it possible to reduce diffusion of heat to other parts.
Patent Document 3 discloses that in a piezoelectric oscillator, a slit-shaped open hole part 16 is formed on a substrate 14 as shown in FIG. 1, so as to restrain a malfunction caused by a difference in an expansion coefficient and to improve frequency temperature behavior.
Patent Document 4 discloses that in a crystal oscillator, band-shaped heating means constituted by a resistance heat generation layer is provided so as to surround an interior region of a substrate along a periphery of the substrate.
Patent Document 5 discloses that in an oven controlled oscillator, a chip resistor 3a for heating is disposed on a blank space 13 of a circuit board 4, which is on a bottom-surface side of a crystal oscillator, a main surface of the chip resistor 3a, on which a resistance coating is formed, is placed so as to face the bottom surface of the crystal oscillator, and the crystal oscillator is disposed on a substrate 4 so as to cover the blank space 13.
[Patent Document 1] Japanese Patent Application Laid-Open No. 2007-214307
[Patent Document 2] Japanese Patent Application Laid-Open No. 08-237031
[Patent Document 3] Japanese Utility Model Application Laid-Open No. 62-037428
[Patent Document 4] Japanese Patent Application Laid-Open No. 2006-014208
[Patent Document 5] Japanese Patent Application Laid-Open No. 2009-284372